Add User Persona Documentation

### Is your feature request related to a problem or challenge?

We recently added a User Persona page in the Ballista documentation. This helps document who Ballista is for, and helps us when reviewing PRs to make sure that we aren't accidentally breaking functionality that different personas depend on.

https://datafusion.apache.org/ballista/contributors-guide/user-personas.html

I would like to do the same for DataFusion "core" next. Let's use this issue to discuss the current personas.

To kick it off, here are few ideas:

- Projects embedding DataFusion for a highly optimized single process query engine
- Projects such as Ballista and DataFusion Distributed, building distributed query engines on top of DataFusion
- Projects building databases
- Python users (data scientists), using the DataFusion Python bindings
- Java users, using the new Java bindings (probably zero users currently)

### Describe the solution you'd like

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### Describe alternatives you've considered

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### Additional context

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